Vacuum gauge



Oct. 9, 1951 E. C. HASS VACUUM GAUGE Filed Sept. 29, 1950 INVENTOR Edward C, Hass BY m# ff. JM

ATTORNEY Patented Oct. 9, 1951 UNITED STATES PATE/NT OFFICE p v n j 2,570,943 v Y.

n "VACUUM GAUGE Edward C. Hasrs`, Prince Georges ICounty, Md. Y l Application September' Z9, 1950,' Serial No. 187,592v

Y l, 1V This invention relates to vacuum gages of the type using a mercury column connected with a body of mercury which is influenced by the vacuum pressure to be measured.

In vacuum gages of this type the mercury column is located inra vertical tube which is sealed at its upper end and is free from gases, the lower end of the tube being connected to a closed cistern containing a body .of mercury and being connected to the source of .vacuum pressure to be measured.

In gages of this type, when operating at low pressures approaching absolute zero, gases are liberated within the gage, and some of these gases find their way into the mercury tube and cause `incorrect. readings. These gases may have different sources, such as leakage of air through the gasket or packing surrounding the lower end of the tube, occluded gases driven off from internal parts of the gage or from impurities in the metal base, and leakage of air through the metal base due to the porosity of the metal.

The main object of the present invention is to devise an improved connection between the;

mercury column tube and the cistern to minimize the possibility of gas entering the tube.

The preferred form of the invention is illustrated in the accompanying drawing which shows a sectional view of the improved connection, the view being taken Von a vertical plane passing through the center of the tube and through the center of the cistern, the mercury tube however being shown in elevation.

Referring to the drawing the base of the gage is a at metal plate I preferably formed of steel. Supported upon the upper face of the plate I is a cistern for the mercury M having a cylindrical wall 2 and a cover 3. The wall 2 may be formed of glass or other transparent materiaLor it may be formed of metal such as steel. The cover plate 3 preferably is formed of metal, and a nipple 4 is threaded into the cover plate for the purpose of `completing a connection from the cistern to the source of vacuum pressure to be measured. Suitable sealing gaskets 2a and 2b are provided between the cylinder 2 and the cover plate 3 and the base plate I respectively for the purpose of rendering the cistern air-tight. y

The lower end of the tube 5V for the mercury column is positioned within a bore or cylindrical vcavity 6 formed in the upper face-of plate I adjacent the cistern 2. The bore 6 extends downwardly to a point near the lower face of the plate I, and the lower end of the tube 5 is seated within a. metal cup 'I which is seated in the bottom 4 claims. (o1. vs -401) A l l Y 2 y of the bore 6. The cup 'I may be formed of dense metal such as steel, and it has a bore sufficiently large to receive the tube 5 and to allow for the usual manufacturing tolerances in the diameter of such tubes.

The lower end of tube 5 is seated in the bottom of the cup by a ground t, that is, the end of the tube is seated in the bottom of the cup by applying grinding material between the ends of` the tube and the bottom of the cup 4and oscillating the tube about its axis until the two engaging surfaces have been ground to be ilat and parallel with each other. After the vgrinding material has been removed from the two surfaces, a very close t would be obtained between the end of the tube 5 and the bottom of the cup 1. f

The tube 5 is secured within the bore 6 by means of a ring of packing material 8 surrounding the tube above the cup 1, and packing gland `9 threaded in the upper end of the bore 6 is provided for compressing the packing ring 8 against the upper edge of cup 'I and into sealing relation with tube 5 and the wall of bore 6. The ring 8 may -be formed of rubber or rubber-like material. The ring isshown in an uncompressed condition in the drawing.

The connection between the lower end of tube 5 and the cistern 2 is completed by means of a counterbore 1a, formed in the center of the bottomrof the cup 1, and the small horizontal bore 'Ib formed radially through the bottom wall of the cup 1 and communicating at its inner end with the bore 'Ia and opening at its outer end into a vertical channel formed by having a portion of the outer face of the cup 'I cut away as shown at lc. This vertical channel communicates at its upper end with an inclined channel or bore I0 formed in the plate I for connecting the bore 6 with a bore II formed in the upper face of plate I within the cistern 2 and immediately below the nipple 4. It is convenient to .form the bore II of conical shape as shown in the drawing, but it could have other circular shapes. A plug I2 having a threaded stem I2a engaging the threaded hole I3 in the plate I below the bore II is provided for the purpose of closing the upper opening of the channel I0 to the cistern 2. A stop screw I4 is threaded into the upper face of plate I, and the head of this screw extends over a radial flange formed on the head of the plug I2 to limit the upward movement of the plug and prevent its removal. The upper face of plug I2 is provided with a transverse slot for receiving a screw-driver which may be inserted through the top of the cistern by removing the nipple 4, it being noted that the plug I2 is located directly beneath the nipple 4.

The construction described above and shown in the drawing is very effective in minimizing the amount of gas that nds its Way into tube 5 when the cistern is subjected to Very low vacuum pressures. The cup 1 serves very important functions in securing this result. For example, it locates` the sealing ring 8 ata considerable distance above the lower end of the tube 5, and it provides a baie over the lower end of the tube 5 so that any gases that are released within the bore 6 are deiiected around the end of the tube and into the lower end of the passage I. Also,

any leakage of air through thev thin-bottomwall of the cavity i5 will not passwthrough the cup 7, because there is no diierential of pressure on opposite sides of the bottom wall of the cup, `but such leakage will pass along the outside of the `bottom of the cup and into the vertical passage connected with the lower end ofthe channel-IB. The. cup a-lso provides; an effectivesealfor the lower end of the tube5 except for thesrnall horizontal bore 'Ib which provides a restricted. passage for the mercury between the tube 5 andthe cistern.

The small size of this passage reduces the possibility of gas entering the tube 5 through the passage, and it also .serves to damp any oscilla.- f

tions of the'mercury within. the tube. when there is a sudden change in pressure applied. to the cistern. I have found that good. results are obtained when the Ybore 'lb has Va diameter .Within the rangeof V0.080-0p090. For eifective. exclu'- sion of gas from the lower end of the-tube 5, it is important that the lower end of channel It shouldopen into the borel` at aY point above .the bore lb'preferably'has close to the `upper endof the cup las possible.

The screw-plug I2 is useful for trapping the mercury within the Vcistern during shipping of the gage. This is accomplishedl by tilting the base plate l in a direction to'drain the mercury from tube -5 through the channel I-r into the cistern, andA after all the mercury has been drained into the cistern plug I2 is. screwedfdown till itseals oif the cavity Il which forms a port onv the upper end of passage lll.V

While I have illustrated and described one form of my invention, it will be obvious thatthe invention is not limited to this specific embodiment and variations in the details of construction are possible within Ythe scopeV of" .the appended claims.

What kIfclaim is:

1. In a vacuumgage, the combination cfa a-t kbase plate having a vertical cylindrical bore formed in the upper face thereof and extending downwardly to a'point near. the lower face thereof, aV mercury cistern supported upon theupper `face of said' plateV adjacentV said bore, saidbase plate havingan inclined passage formed; therein with theupper end of the passage opening into said cistern andthe lower-fend opening intosaid bore near. the top thereof, a cupv seated in said bore` and. extending above the opening' of said inclined passage into said bore.. and: having ra channel for-ined in the outer surface thereof frornsaid .opening to the bottomrofvsaidbore, -a Y verticalltubehaving the lower endV thereof seated 4 in said cup, a packing ring surrounding said tube above said cup, a gland arranged in the upper end of said bore and pressing said packing ring against the upper edge of said cup, and said cup having a small radially extending bore formed in the bottom wall thereof with its outer end opening into said vertical channel and its inner end communicating with the inner space of said tube through a port formed in the upper face of ,the bottom wall of said cup.

2. In a vacuum gage, the combination of a flat `base plate having a vertical cylindrical bore formed in the upper face thereof and extending downwardly to a point near the lower face thereofl a mercury cistern supported upon the upper face ofsaidfplate adjacent said bore, said base plate. having. an inclined passage formed therein with the upper end of the passage opening into said cistern and the lower end opening into said bore near the'top thereof, a cup seated inzsaidrbcre and extending above the openine'of said inclinednassageintosaid bore and having a Channel formed inl the outer surface thereof from said opening to -thesbottornrofY said bo vertical tube havingzthe lower end thereof .se Ated in said .cup,a:'packing ringsurrounding said tube above said cup. and sealing said tube withinv said boreand said cup having a-srnall radially ex.- tendingbore .formed inthe :bottom wall thereof with Yits..outer end .opening intoy said. vertical channel and its inner end communicating with the inner` space .ofsaid tube througha yport formed in the. upperfaceof .the/.bottom wall of saidcupl Y3. Ina vacuumfgage, theicombination of.a;.flat base plate having. a vertical cylindrical. bore formed-'in the upperV face :thereof and extending downwardly. to a pointinearthe lower facethere: of,-aY mercury cistern. supported. upon the upper face-of saidplate adjacent saidY bore, said. base plate having anY inclinedl passage .formed therein with the upper end .ofi the passage opening into said cistern andithe lower. end opening intosaid bore nearthe topthereof, a cup seated. Vinsaid bor-e, 'averticaltubehavingithe lower end there:- of seated in said cup, the openingofsaid passage intosaid' boreand lsealing said tubein. saidbore, a packing ring surrounding. saidy tube a'bove the lower .end of said tube being. positionedbelow the opening .of said` inclined passage. into. said bore, and-,saidzcup having av .smallradially extending .bore formed in the. .bottom wall. thereof :withits outer end opening into. said; boreand .its inner end communicating withA .the innerfspaceofi said tube through a port. formed inthe upper Vface of the `bottom wall of "said cup.

4. A.. vacuum gage.. according. to claim v3.1where.- inthe lowerend of said tube-.is seatedon the bottom Wall.. of :said cnprbyv ai ground fit.

EDWARD HASS.

REFERENCES, CITED Therfollowingv referencesare of recordY in the fileA of this patent:

UNrrED STATES PATENTS 

